Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$138.72	12.107%	$155.5148	$155.51	$155.50	$155.50
Purchase #2	$44.58	11.165%	$49.5574	$49.56	$49.55	$49.60
Purchase #3	$62.42	11.567%	$69.6401	$69.64	$69.65	$69.60
Purchase #4	$233.66	13.528%	$265.2695	$265.27	$265.25	$265.30
Purchase #5	$187.57	3.860%	$194.8102	$194.81	$194.80	$194.80
Purchase #6	$67.90	5.706%	$71.7744	$71.77	$71.75	$71.80
Purchase #7	$221.32	13.368%	$250.9061	$250.91	$250.90	$250.90
7 purchase totals =	$956.17		$1,057.4725	$1,057.47	$1,057.40	$1,057.50